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authorNeilBrown <neilb@suse.de>2011-12-22 18:17:51 -0500
committerNeilBrown <neilb@suse.de>2011-12-22 18:17:51 -0500
commit2d78f8c451785f030ac1676a18691896b59c69d8 (patch)
tree4dfe69115b2ca2fb8be2a671e7c8399c3925fcb9 /Documentation
parentb8321b68d1445f308324517e45fb0a5c2b48e271 (diff)
md: create externally visible flags for supporting hot-replace.
hot-replace is a feature being added to md which will allow a device to be replaced without removing it from the array first. With hot-replace a spare can be activated and recovery can start while the original device is still in place, thus allowing a transition from an unreliable device to a reliable device without leaving the array degraded during the transition. It can also be use when the original device is still reliable but it not wanted for some reason. This will eventually be supported in RAID4/5/6 and RAID10. This patch adds a super-block flag to distinguish the replacement device. If an old kernel sees this flag it will reject the device. It also adds two per-device flags which are viewable and settable via sysfs. "want_replacement" can be set to request that a device be replaced. "replacement" is set to show that this device is replacing another device. The "rd%d" links in /sys/block/mdXx/md only apply to the original device, not the replacement. We currently don't make links for the replacement - there doesn't seem to be a need. Signed-off-by: NeilBrown <neilb@suse.de>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/md.txt22
1 files changed, 18 insertions, 4 deletions
diff --git a/Documentation/md.txt b/Documentation/md.txt
index fc94770f44ab..993fba37b7d1 100644
--- a/Documentation/md.txt
+++ b/Documentation/md.txt
@@ -357,14 +357,14 @@ Each directory contains:
357 written to, that device. 357 written to, that device.
358 358
359 state 359 state
360 A file recording the current state of the device in the array 360 A file recording the current state of the device in the array
361 which can be a comma separated list of 361 which can be a comma separated list of
362 faulty - device has been kicked from active use due to 362 faulty - device has been kicked from active use due to
363 a detected fault or it has unacknowledged bad 363 a detected fault, or it has unacknowledged bad
364 blocks 364 blocks
365 in_sync - device is a fully in-sync member of the array 365 in_sync - device is a fully in-sync member of the array
366 writemostly - device will only be subject to read 366 writemostly - device will only be subject to read
367 requests if there are no other options. 367 requests if there are no other options.
368 This applies only to raid1 arrays. 368 This applies only to raid1 arrays.
369 blocked - device has failed, and the failure hasn't been 369 blocked - device has failed, and the failure hasn't been
370 acknowledged yet by the metadata handler. 370 acknowledged yet by the metadata handler.
@@ -374,6 +374,13 @@ Each directory contains:
374 This includes spares that are in the process 374 This includes spares that are in the process
375 of being recovered to 375 of being recovered to
376 write_error - device has ever seen a write error. 376 write_error - device has ever seen a write error.
377 want_replacement - device is (mostly) working but probably
378 should be replaced, either due to errors or
379 due to user request.
380 replacement - device is a replacement for another active
381 device with same raid_disk.
382
383
377 This list may grow in future. 384 This list may grow in future.
378 This can be written to. 385 This can be written to.
379 Writing "faulty" simulates a failure on the device. 386 Writing "faulty" simulates a failure on the device.
@@ -386,6 +393,13 @@ Each directory contains:
386 Writing "in_sync" sets the in_sync flag. 393 Writing "in_sync" sets the in_sync flag.
387 Writing "write_error" sets writeerrorseen flag. 394 Writing "write_error" sets writeerrorseen flag.
388 Writing "-write_error" clears writeerrorseen flag. 395 Writing "-write_error" clears writeerrorseen flag.
396 Writing "want_replacement" is allowed at any time except to a
397 replacement device or a spare. It sets the flag.
398 Writing "-want_replacement" is allowed at any time. It clears
399 the flag.
400 Writing "replacement" or "-replacement" is only allowed before
401 starting the array. It sets or clears the flag.
402
389 403
390 This file responds to select/poll. Any change to 'faulty' 404 This file responds to select/poll. Any change to 'faulty'
391 or 'blocked' causes an event. 405 or 'blocked' causes an event.